Method and apparatus for delivery notification of non-access stratum retransmission

ABSTRACT

A method and apparatus for data delivery confirmation in a wireless transmit receive unit (WTRU) including transmitting an uplink (UL) message, performing a mobility operation, determining that the UL message is not acknowledged, and generating a delivery failure message. The mobility operation is a handover or a radio resource control (RRC) connection reestablishment. A message including the delivery failure message is passed between protocol layers.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/057,394 filed May 30, 2008, which is incorporated by reference as iffully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

The Third Generation Partnership Project (3GPP) has initiated the LongTerm Evolution (LTE) program to bring new technology, new networkarchitecture, new configurations and new applications and services towireless networks in order to provide improved spectral efficiency andfaster user experiences. FIG. 1 shows an overview of an EvolvedUniversal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess Network (E-UTRAN) 100 in accordance with the prior art. As shownin FIG. 1, E-UTRAN 100 includes three eNodeBs (eNBs) 102, however, anynumber of eNBs may be included in E-UTRAN 100. The eNBs 102 areinterconnected by an X2 interface 108. The eNBs 102 are also connectedby an S1 interface 106 to the Evolved Packet Core (EPC) 104. The EPC 104includes a Mobility Management Entity (MME) 108 and a Serving Gateway(S-GW) 110.

FIG. 2 shows an LTE user-plane protocol stack 200 in accordance with theprior art. The protocol stack 200 is located in a WTRU 210 and includesthe packet data control protocol (PDCP) 202, the radio link control(RLC) 204, the medium access control (MAC) 206 and the physical layer(PHY) 208. The protocol stack 200 may also reside in an eNB (not shown).

FIG. 3 shows an LTE control plane protocol stack 300 in the WTRU 210 ofFIG. 2. The control plane protocol stack 300 includes the non-accessstratum (NAS) 302 and a radio resource control (RRC) 304. Also includedare the PDCP 306, RLC 308 and MAC 310, which together form the layer 2sublayer 312.

During a handover a WTRU 210 may transmit uplink (UL) system data units(SDUs) from the PDCP (206). If the WTRU 210 does not receive a noticethat the SDUs were successfully delivered, the WTRU 210 may retransmitthe SDUs. The WTRU 210 may use a PDCP status report, received from aneNB, to determine which uplink PDCP SDUs to retransmit. The WTRU 210 mayalso use the report to discard SDUs, if the SDUs were received oracknowledged by the status report.

During a handover, a target eNB may retransmit, to the WTRU 210,downlink PDCP SDUs that were forwarded by a source eNB. The WTRU 210 maytransmit a PDCP status report to the target eNB. The target eNB mayutilize the PDCP status report to determine which PDCP SDUs toretransmit to the WTRU 210. The target eNB may also discard downlinkPDCP SDUs, if the SDUs were received or acknowledged by PDCP statusreport. Once the WTRU 210 receives the SDUs, the WTRU 210 may reorderthe SDUs and eliminate duplicates. The WTRU 210 may then deactivate anyfunctions based on a timer, such as a flush timer, for example. Forsignaling radio bearers (SRBs), the RLC 204 may indicate that handoverhas occurred and the PDCP 202 may reinitialize state variables such as aPDCP sequence number (SN) and a hyper frame number (HFN). The statevariables may also be set to zero. All PDCP SDUs and PDCP PDUs that havebeen previously stored may be discarded.

In order to perform NAS level retransmission, the access stratum (AS)(not shown) may provide an indication of an NAS message transmissionfailure, if the failure occurred due to handover or cell selection.

SUMMARY

A method and apparatus is disclosed for data delivery confirmation in awireless transmit receive unit (WTRU). This may include transmitting anuplink (UL) message, performing a mobility operation, determining thatthe UL message is not acknowledged, and generating a delivery failuremessage. The mobility operation may be a handover or a radio resourcecontrol (RRC) connection reestablishment. A message including thedelivery failure message may be passed between protocol layers to anon-access stratum layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an overview of an E-UTRAN in accordance with the prior art;

FIG. 2 shows an LTE user-plane protocol stack in accordance with theprior art;

FIG. 3 shows an LTE control-plane protocol stack in accordance with theprior art;

FIG. 4 shows an example wireless communication system including aplurality of WTRUs and an eNB in accordance with one embodiment;

FIG. 5 is a block diagram of a WTRU and the eNB of FIG. 4;

FIG. 6A is a block diagram of an RRC level acknowledgement method inaccordance with one embodiment;

FIG. 6B is a block diagram of an RRC level acknowledgement method inaccordance with an alternative embodiment;

FIG. 6C is a block diagram of an RRC level acknowledgement method inaccordance with another embodiment;

FIG. 7 is a block diagram of a method of direct notification of deliveryin accordance with one embodiment;

FIG. 8 is a block diagram of a notification method 800 in accordancewith one embodiment; and

FIG. 9 is a block diagram of a notification method 900 in accordancewith another embodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment. Furthermore, the terms “delivery notification”, “deliveryconfirmation”, “delivery indication”, “transmission confirmation”, and“transmission indication”, are used interchangeably hereinafter.

As used herein, the terms “upper layer” and “lower layer” are relativeterms. Each layer in a protocol stack, including the NAS, RRC, PDCP,RLC, and MAC, is an upper layer in relation to any layer below it in theprotocol stack. Therefore, for example, the NAS would be an upper layerin relation to the RRC, PDCP, RLC and MAC layers whereas the RLC is onlyan upper layer in relation to the MAC layer.

FIG. 4 shows a wireless communication system 400 including a pluralityof WTRUs 410 and an e Node B (eNB) 420. As shown in FIG. 4, the WTRUs410 are in communication with the eNB 420. Although three WTRUs 410 andone eNB 420 are shown in FIG. 4, it should be noted that any combinationof wireless and wired devices may be included in the wirelesscommunication system 400.

FIG. 5 is a functional block diagram 500 of a WTRU 410 and the eNB 420of the wireless communication system 400 of FIG. 4. As shown in FIG. 4,the WTRU 410 is in communication with the eNB 420. The WTRU 410 isconfigured with both a user plane protocol stack (100 of FIG. 1) andcontrol plane protocol stack (200 of FIG. 2). Each component in a stackis configured to communicate with components above and below it in thestack. Furthermore, each component in a stack is configured tocommunicate with its peer component in a peer protocol stack.

In addition to the components that may be found in a typical WTRU, theWTRU 410 includes a processor 515, a receiver 516, a transmitter 517,and an antenna 518. The WTRU 410 may also include a user interface 518,which may include, but is not limited to, an LCD or LED screen, a touchscreen, a keyboard, a stylus, or any other typical input/output device.The WTRU 410 may also include memory 519, both volatile and non-volatileas well as interfaces 520 to other WTRU's, such as USB ports, serialports and the like. The receiver 516 and the transmitter 517 are incommunication with the processor 515. The antenna 518 is incommunication with both the receiver 516 and the transmitter 517 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical eNB, theeNB 420 includes a processor 525, a receiver 526, a transmitter 527, andan antenna 528. The receiver 526 and the transmitter 527 are incommunication with the processor 525. The antenna 528 is incommunication with both the receiver 526 and the transmitter 527 tofacilitate the transmission and reception of wireless data.

A WTRU and an eNB may operate in acknowledge mode (AM) or unacknowledgedmode (UM). When operating in AM, a transmitting entity may receive anacknowledgment if a data packet, such as a PDU or an SDU, issuccessfully transmitted to a receiving entity. For example, an RLCentity may generate a data packet and the packet may be transmitted. Thereceiving RLC entity may receive the packet and may generate an RLCstatus report that may be transmitted back to the transmitting RLCentity. The RLC status report may include an indication to show iftransmission of the packet was successful. For example, if a WTRUtransmits a set of RLC PDUs, and all the transmitted RLC PDUs wereacknowledged by the receiving entity in an RLC status report, thendelivery may be deemed successful. However, if one of the RLC PDUs wasnegatively acknowledged, and the packet was not retransmitted or isdiscarded, then the transmitting entity may receive an RLC status reportthat includes an indication of unsuccessful delivery.

Another indication that the RLC PDU was not successfully delivered maybe provided to the transmitting RLC entity without a status report. Forexample, if the RLC entity has been reset or reestablished and at leastone RLC packet has been negatively acknowledged or has not beenpositively acknowledged by the receiving RLC, the transmitting RLC maydetermine that delivery was not successful.

A PDCP may send a packet to an RLC. The RLC may transmit the packet andsend an RLC delivery confirmation to the PDCP. If the PDCP originallyreceived the packet from an upper layer, such as an RRC for example, thePDCP may provide a delivery indicator to the upper layer. An indicationof successful delivery of the PDCP packet may be an indicator providedby the RLC entity. The PDCP may provide the indicator to the upperlayer, such as the RRC, for example, if it receives an indication ofsuccess from the lower layer, such as the RLC, for example. The PDCP maytransmit an indication of unsuccessful delivery if the PDCP receives afailure notification from the lower layer. Furthermore, an indication ofdelivery failure may be provided to the RRC from the PDCP, if the PDCPdiscards the packet prior to submitting it to the RLC layer.

The PDCP status report function may be used to determine the status ofthe delivery of a PDCP packet. An SRB that supports NAS messages mayalso support the exchange of PDCP status reports. The SRB may be used toconvey information on missing or acknowledged PDCP packets.

In a handover, the PDCP status report may be used to determine thestatus of the delivery of a PDCP SDU. Each PDCP SDU has an associatedsequence number. The PDCP sequence number (SN) associated with the firstSDU to be transmitted to the target cell after handover may be continuedfrom the SN of the last SDU delivered to the source cell beforehandover. In other words, the SNs are continued from the source to thetarget, rather than starting with a new SN in the target cell. The SRBuplink (UL) and/or downlink (DL) PDCP sequence number (SN) context canbe exchanged between the source and the target eNB. The PDCP SN may alsobe retained in the WTRU. Alternatively, a WTRU or eNB may create thePDCP status report using the pre-handover SN. As another alternative,the PDCP status report may be exchanged in the source eNB.

PDCP status reports for SRBs provide delivery confirmation to upperlayers, such as an RRC and NAS, for example. The upper layer will thentake the appropriate action, based on the status report.

The RRC may also provide a delivery notification service to upperlayers. FIG. 6A is a block diagram of an RRC level acknowledgementmethod 600 in accordance with one embodiment. The NAS 602 passes amessage 604 to the RRC 606. The RRC 606 processes the message 604 andpasses an RRC message 608 to the PDCP 610. The PDCP 610 passes a PDCPSDU 614 to lower layers for transmission. The PDCP 610 may pass adelivery status indicator 612 to the NAS 602 that includes an indicationif the delivery of the PDCP SDU 614 was successful or unsuccessful. Theindicator 612 may show a successful delivery if the PDCP 610 receives anindication that delivery of the PDCP SDU 614 was successful. However, ifthe PDCP 610 does not receive an acknowledgement (ACK) or receives anon-acknowledgement (NACK), the PDCP 610 may determine that delivery ofthe PDCP SDU 614 was not successful, and the delivery status indicator612 will indicate an unsuccessful delivery.

FIG. 6B is a block diagram of an RRC level acknowledgement method 620 inaccordance with another embodiment. In FIG. 6A, the RRC 606 relies onthe PDCP 608 to provide delivery notification to the NAS 602. As shownin FIG. 6B, the RRC 606 may also directly provide delivery notificationto the NAS 602. Similar to FIG. 6A, in FIG. 6B the NAS 602 passes amessage 604 to the RRC 606. However, unlike in FIG. 6A, in FIG. 6B theRRC 606 sends a message 624 directly to a peer RRC 622. If the RRC 606does not receive an RLC Layer 2 (L2) ACK (not shown) for the directtransfer message 624, the RRC 606 may send a delivery notification 626directly to the NAS 602 that indicates a failed delivery. In response tothe delivery notification 626, the NAS 602 may stop all timers andretransmit the message 604. The RRC 606 may also provide the deliverynotification 626 to the NAS 602 if the RRC 606 receives an indication toretransmit the NAS message in a handover command or through additionalsignaling in the source or target cell.

Upon receiving a handover command or upon executing a handover or cellselection or reselection, the RRC 606 may provide a deliverynotification 626 to the upper layer, for example, the NAS 602 or tolower layers, for example, the PDCP 610. The notification may include anotice that the RRC 606 received the handover command, or executed ahandover, cell selection or cell reselection. The RRC 606 may alsoprovide a notification of another event that may trigger a NAS 602retransmission or delivery notification to the NAS 602 or the PDCP 610.

FIG. 6C is a block diagram of an RRC level acknowledgement method 630 inaccordance with an alternative embodiment. The RRC 606 sets a bit in aheader of an RRC message 632 to request an RRC level acknowledgementfrom a peer RRC entity 622. The peer RRC entity 622 then sends an RRClevel acknowledgment 636. If no acknowledgment is received within acertain time, a delivery notification of failed transmission 634 isprovided to the NAS 602 at handover. A lack of acknowledgement from thepeer RRC entity 622 may also be used to trigger RRC levelretransmission.

The RRC acknowledgment 636 from the RRC peer entity 622 may be forsingle or multiple RRC messages. The RRC 606 may request that the peerRRC 622 send the acknowledgement 636 by setting a bit in an RRC headeror the acknowledgment 636 may be required by definition or default. TheRRC acknowledgment 636 may indicate which instance of a particular RRCmessage is being acknowledged.

A delivery confirmation to an upper layer may be triggered by a lowerlayer upon a final determination of whether the SDU has beensuccessfully delivered or of a transmission failure. A timer may be usedto delay the delivery confirmation. For example, a delivery confirmationprohibit timer may be running. The delivery confirmation may not occurwhile the timer is running. However, if a trigger occurs and the timerhas expired, the delivery confirmation may be passed on to the higherlayer.

A delivery confirmation to an upper layer may also be triggered by lowerlayer upon a mobility event, such as a handover, a reset or areestablishment event, for example. Further, the delivery confirmationmay be triggered upon a request from an upper layer.

FIG. 7 is a block diagram of a method of direct notification of delivery700 in accordance with one embodiment. The NAS 702 may send a message704 to the RRC 706. Upon sending the message 704, the NAS 702 mayindicate to the RRC 706 if the NAS 702 wants a delivery confirmation.The NAS 702 may, based on notifications received from the RRC 706 and/orthe PDCP 708, immediately retransmit the message 704, stop a timer 712that started when the message 704 was sent originally, or decrease orincrease timer 712. Upon retransmission of the message 704, the NAS 702may start a new timer 714.

Upon receiving the NAS message 704 from the NAS 702, the RRC 706examines the message 704, which may include a delivery status requestindicator (not shown) to determine if a delivery confirmation isrequired for the message 704. If a delivery confirmation is required,the RRC 706 submits an RRC message 720 that includes the NAS message704, to the PDCP 708 that optionally includes a delivery confirmationrequest.

The PDCP 708 receives the RRC message 720 that may include the deliveryconfirmation request and determines if a delivery confirmation isrequired for the message 720. If delivery confirmation is required, thePDCP 708 submits a message 722 to the RLC 724. The PDCP 708 indicates,with the message 722, if the PDCP 708 requires a delivery confirmation.The PDCP 708 sends message 722 to the RLC 724, and if a handover commandis received, the PDCP 708 may also exchange PDCP status reports 726 witha peer PDCP 728 that pertain to the SRBs for handover. The PDCP 708 mayalso exchange PDCP status reports 726 with the peer PDCP 728 if there isa cell selection or reselection. Alternatively, if message 722 is sent,a new polling bit may be set in the PDCP header of the message 722. Thepolling bit will solicit the peer PDCP entity 728 to generate a PDCPstatus report 726.

The RLC 724 receives the message 722 from the PDCP 708 and determines ifthe message 722 includes a requirement for delivery confirmation. If themessage 722 includes a delivery confirmation request, the RLC 724 willset the RLC status report polling bit in the RLC header of the message.The RLC status report polling bit will indicate to the peer RLC entity730 that a status report 732 should be generated.

FIG. 8 is a block diagram of a notification method 800 in accordancewith one embodiment. The NAS 802 sends an RRC SDU 812 to the RRC 804.The RRC SDU 812 includes a delivery confirmation request. The RRC 804processes the RRC SDU 812 and sends a PDCP SDU 814 to the PDCP 806. ThePDCP SDU 814 includes a delivery confirmation request. The PDCP 806processes the PDCP SDU 814 and sends an RLC SDU 816 to the RLC 808. Whena handover occurs, the PDCP 806 will send and receive PDCP statusreports 822 to and from a peer PDCP 824 in a target cell. The deliverystatus of the PDCP SDU 814 is included in the PDCP status report 822.The PDCP 806 sends a delivery status report 826 to the RRC 804. The RRC804 then forwards the delivery status report 826 to the NAS 802.

FIG. 9 is a block diagram of a notification method 900 in accordancewith another embodiment. In FIG. 9, the NAS 902 submits an RRC SDU 912to the RRC 904. The RRC SDU 912 includes a delivery confirmationrequest. The RRC 904 processes the RRC SDU 912 and creates and submits aPDCP SDU 914 to the PDCP 906. The PDCP SDU 914 may include a deliveryconfirmation request. The PDCP 906 processes the PDCP SDU 914 andcreates and submits an RLC SDU 916 to the RLC 906. The RLC 908 processesthe RLC SDU 916 and creates and submits at least one MAC SDU 918 to theMAC 910. The RLC 908, while functioning in AM mode, may receive anACK/NACK 920 from a peer RLC entity 922. The RLC 908 then provides adelivery status report 924 to the PDCP 906 based on the latest RLCdelivery status, which is derived from the ACK/NACK 920. The PDCP 906provides the delivery status report 924 to the RRC 904. The RRC 904provides the delivery status report 924 to the NAS 902.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method of data delivery notification in a wireless transmit/receiveunit (WTRU), the method comprising: transmitting an uplink (UL) message;starting a timer in response to transmitting the UL message; performinga mobility operation prior to expiration of the timer; wherein anindication of delivery failure is sent to a radio resource control (RRC)layer by a lower layer in response to a status report associated withthe timer; and communicating, by the RRC layer, a delivery failuremessage to the non-access stratum (NAS) in response to performing themobility operation even when the indication of the delivery failure isnot sent to the RRC.
 2. The method as in claim 1 wherein the mobilityoperation is a handover.
 3. The method as in claim 1 wherein themobility operation is a RRC connection reestablishment.
 4. The method asin claim 1 wherein the generation of the delivery failure message isbased on an event between peer components on a protocol stack.
 5. Themethod as in claim 4 wherein the event is the reception of a statusreport, an acknowledgement, a negative acknowledgement or an expirationof a timer.
 6. A wireless transmit/receive unit (WTRU) comprising: aprocessor configured to: transmit an uplink (UL) message; start a timerin response to transmitting the UL message; perform a mobility operationprior to expiration of the timer; wherein an indication of deliveryfailure is sent to a radio resource control (RRC) layer by a lower layerin response to a status report associated with the timer; andcommunicate, by the RRC layer, a delivery failure message to thenon-access stratum (NAS) in response to performing the mobilityoperation even when the indication of the delivery failure is not sentto the RRC.
 7. The WTRU as in claim 6 wherein the mobility operation isa handover.
 8. The WTRU as in claim 6 wherein the mobility operation isa RRC connection reestablishment.
 9. The WTRU as in claim 6 wherein thegeneration of the delivery failure message is based on an event betweenpeer components on a protocol stack.
 10. The WTRU as in claim 9 whereinthe event is the reception of a status report, an acknowledgement, anegative acknowledgement or an expiration of a timer.